1. Field of the Invention
The present application relates to image forming apparatus such as copying machines, printers and facsimile machines. More particularly, the present application relates to image forming apparatus in which the rotation of a plurality of image bearing members is more evenly matched to maintain even toner distribution and improve image quality.
2. Description of the Related Art
In so-called tandem type image forming apparatus, four image bearing members on which latent images of different colors are formed, are disposed in parallel along a conveying direction of a recording sheet. With such known image forming apparatus, color images are formed on recording sheets as they pass each image bearing member in the conveying direction.
FIGS. 15 and 16 are side elevational and top plan views showing an exemplary construction of a drive power transmission mechanism for the image bearing members in the above-mentioned image forming apparatus. Gears 3B, 3M, 3Y and 3C are mounted at an end portion of each rotational shaft of photoconductive elements 1B, 1M, 1Y and 1C used as the image bearing members. Gear 3C of the photoconductive element 1C is engaged with a drive gear 10 of a motor 9 provided as a drive power source. Intermediate gears 28 are disposed between the gears of each photoconductive element, as seen in FIG. 15. As the motor 9 rotates, a drive power is translated to each photoconductive element via the gears of the photoconductive elements and the intermediate gears, so that the photoconductive elements 1B, IM, 1Y and 1C rotate at the same time.
Additional configurations of the drive power transmission mechanisms for image forming apparatus provided with a plurality of image bearing members are known. For example, in Japanese Laid-Open Patent Application No. 167858/1994, the gears of each rotating image bearing members are inter-connected via intermediate gears which transmit drive power with a high reduction speed ratio.
In Japanese Laid-Open Patent Application No. 7-209947, the drive power transmission mechanism is provided with the drive gear of the drive power source which is engaged with a drive gear of the photoconductive element disposed adjacent to the drive power source, and a driven gear in which rotation transmitted from the drive gear is further transmitted to the driven gear of the other photoconductive elements via an intermediate gear.
Further, FIG. 17 illustrates a drive power transmission mechanism in which a toothed timing belt 40 is used to translate rotational movement of the motor to the image bearing members. This is known drive power transmission mechanism is composed of pulleys 41C, 41Y, 41M and 41B mounted on an end of the rotating shafts of the photoconductive elements 1C, 1Y, 1M and 1B, an idler 42, a timing belt 40, an idler 43, a tension pulley 44, a drive pulley 45 and a drive motor 9.
One drawback to the drive power transmission mechanism shown in FIGS. 15 and 16, is that rotation of the photoconductive elements may become uneven which may result in a line of the location of the gears defining a drive power transmission path for the image bearing members that is too long. As a result, an unevenness of rotation between photoconductive element 1C and 1B may occur, which may result in an unevenness of the image density
Further, the drive power transmission mechanism disclosed in the aforementioned Japanese Laid-Open Patent Application No. 6-167858 discusses that accumulation of the unevenness of rotation can be limited by using intermediate gears. However, in this construction, the line defining the drive power transmission path is too long so that the transmissibility of the drive power from gear to gear may deteriorate. Furthermore, machines with large drive power transmission paths tend to generate noise caused by the meshing of the gears.
In addition, when a timing belt is used, as shown in FIG. 17, even though the engagement between the timing belt 40 and each driven pulley reaches a smooth state, an unevenness of rotation (or vibration) of the photoconductive elements cannot be completely avoided because irregularities in the engagement between the belt and pulleys often occurs. When the photocoductive elements vibrate, the density of the image becomes uneven so that banding appears in the image, and possibly the quality of the image deteriorates.